In a manufacturing process of a semiconductor device or a liquid crystal display device, a plasma processing apparatus such as a plasma etching apparatus and a plasma CVD film forming apparatus has been employed to perform a plasma process, e.g., an etching process or a film forming process, on a substrate to be processed such as a semiconductor wafer and a glass substrate.
There are well-known plasma generating methods used in the plasma processing apparatus, e.g., a method including steps of supplying a processing gas into a chamber with parallel plate electrodes disposed therein; feeding a specific power to the parallel plate electrodes; and generating a plasma by capacitive coupling between the electrodes and a method including steps of accelerating electrons by an electric field produced by a microwave which is introduced into a chamber and a magnetic field generated by a magnetic field generating unit which is installed outside the chamber; colliding the accelerated electrons with neutral molecules of a processing gas; and generating a plasma by ionization of the neutral molecules, or the like.
In the latter method utilizing a magnetron effect due to the electric field produced by the microwave and the magnetic field generated by the magnetic field generating unit, a predetermined specific power microwave is supplied to an antenna disposed in the chamber through a waveguide/coaxial tube so that the microwave is emitted into a processing space in the chamber.
FIG. 8 is an explanatory diagram showing a schematic configuration of a typical, conventional microwave introducing unit. The microwave introducing unit 90 includes a microwave oscillator 91 having a magnetron 91a for outputting a microwave whose power is regulated to be close to a predetermined specific value and a microwave generating power supply 91b for supplying an anode current of a predetermined frequency to the magnetron 91a; an antenna 94 for emitting a microwave which is outputted from the microwave oscillator 91 into a processing space in a chamber; an isolator 92 for absorbing a reflected microwave returning to the microwave oscillator 91 from the antenna 94; and a matcher 93 which has a tuner for performing matching for the antenna 94 to diminish a power of the reflected microwave and connects a waveguide to a coaxial tube (see, e.g., Japanese Patent No. 2722070 and Japanese Patent Laid-Open Application No. H8-306319).
However, the microwave oscillator 91 using the magnetron 91a has a drawback such as the high cost for the equipment and the maintenance thereof due to a short life of about half a year of the magnetron 91a. Further, since the magnetron 91a has oscillation stability of approximately 1% and output stability of approximately 3%, resulting in a large difference therebetween, it is difficult to transmit a stable microwave.
The present invention has been conceived to overcome the above drawbacks; and it is, therefore, an object of the present invention to provide a plasma processing apparatus provided with a microwave oscillator having a long life. Further, it is another object of the present invention to provide a plasma processing apparatus provided with a microwave oscillator capable of stably supplying a microwave.
First, in order to overcome the above drawbacks, the present inventors have proposed a plasma processing apparatus for amplifying the microwave to have a predetermined specific output by using a semiconductor amplifying device (Patent Application No. 2002-288769, hereinafter, referred to as “prior application”). FIG. 7 is an explanatory diagram showing a schematic configuration of a microwave introducing unit provided with a microwave oscillator using a semiconductor amplifying device of the prior application.
The microwave introducing unit 80 includes a microwave oscillator 80a for oscillating to generate the microwave of a predetermined specific power; an isolator 85 for absorbing a microwave, among the microwaves outputted from the microwave oscillator 80a, which returns to the microwave oscillator 80a from the antenna 87; an antenna 87 provided in a chamber for emitting a microwave which is outputted through the isolator 85 into a processing space in the chamber; and a matcher 86 for performing matching for the antenna 87 to reduce the microwave reflected from the antenna 87.
Further, the microwave oscillator 80a includes a microwave generator 81 for generating the microwave; a divider 82 for dividing the microwave outputted from the microwave generator 81 into a plurality of microwaves, e.g., into four to be distributed along four paths as shown in FIG. 7; four solid state amplifiers 83, each amplifying a corresponding one of four path microwaves outputted from the divider 82 to have a predetermined specific power; and a combiner 84 for combining the four amplified microwaves respectively amplified in solid state amplifiers 83.
The microwave generator 81 has a microwave generating source (generator) 81a for generating a microwave of a predetermined frequency (e.g., 2.45 GHz) and a variable attenuator 81b for attenuating a power of the microwave generated by the microwave generating source 81a to a specified level.
Each solid state amplifier 83 has a sub-divider 83a for further dividing an input microwave into a plurality of microwaves (four shown in FIG. 7); a plurality of semiconductor amplifying devices 83b for amplifying the respective microwaves outputted from the sub-divider 83a to have respectively predetermined specific powers; a sub-combiner 83c for combining amplified microwaves outputted from semiconductor amplifying devices 83b. 
By using such microwave introducing unit wherein each semiconductor amplifying device 83b performs power amplification, the apparatus becomes semipermanent and a microwave of a stable output power can be emitted into the chamber.
However, in such microwave introducing unit 80, there is a need to perform impedance matching in the divider 82 and the combiner 84, in addition to impedance matching in the solid state amplifier 83. In case of impedance mismatching, power loss can be increased. Particularly, there is a need to transmit the microwave of 2 to 3 kW to, e.g., the antenna 87 in a plasma processing apparatus and the combiner 84 is required to combine the microwaves of large power in the microwave introducing unit 80. For this reason, especially, in the combiner 84, a more precise impedance matching is required to suppress the power loss of the microwave.
Further, in order to transmit the large power microwave outputted from the combiner 84 to the isolator 85, the isolator 85 needs to be large-sized in a few KW range, resulting in restricting the place where the isolator 85 is to be installed and further resulting in a high cost for the isolator 85 itself. Furthermore, since the combined microwave is transmitted to the antenna 87 through a single coaxial tube, it is not possible to control the distribution of the microwave outputted from the antenna 87.